How to create a workable leaf spring in Blender?
This is the closest simulation I could think of (also made video version available):


Create a Cube Shift+amc and scale down it sz.1Returnsx.5Return.
Create and instance with Alt+dy2Return. Repeat several times with Shift+r, making sure to end with an uneven amount.
Select all newly created cubes and and make active rigid bodies Control+r.
In the the Tool Shelf under Rigid Body Tools, click Calculate Mass and select Steel.
One by one go along selecting each of the neighbouring cubes and click the Connect button (also in the Rigid Body Tools).
Finally select the centre cube and set it to passive Control+Shift+r.